Polymeric Materials PDF

Ch3: Polymeric Materials Dr Nur Nabilah Shahidan Room: Bsp 2.18 This Photo by Unknown Author is licensed under CC BY-NC-ND ...

Ch3: Polymeric Materials Dr Nur Nabilah Shahidan Room: Bsp 2.18 This Photo by Unknown Author is licensed under CC BY-NC-ND  FR Outline 7.1. Polymerization and Properties of polymers 7.2. Effect of Structural Modification and Temperature on Properties of polymers 7.3. High-Strength Thermoplastics Add a footer 2  FR 7.1. Polymerization and Properties of polymers Add a footer 3  FR What is a Polymer ? —M—M—M—M—M—M— or —(M)n— Many repeating units POLYMER : A large molecule made up of small building blocks (monomers) MONOMER : building block  FR Definitions of Common Polymer Terms a) Repeating Unit Conventional Repeating unit depends on monomer used in synthesis, e.g. The Base Unit is independent to synthetic route and is smallest possible Repeating Unit b) Degree of Polymerization, DP DP = average number of repeat units per chain Mn DP = m where m = repeat unit molecular weight Eg: for PVC: m = 2(carbon) + 3(hydrogen) + 1(Clorine) (from periodic table) = 2(12.011) + 3(1.008) + 1(35.45) = 62.496 g/mol if Mn of PVC is 21,150 g/mol, DP = 21,150 / 62.496 = 338.42 6  FR Definitions of Common Polymer Terms c) End groups: structural units that terminate polymer chains d) Living Polymers Telechelic Polymers Macromonomers or Oligomers containing reactive end groups capable of undergoing polymerisation, usually by heating, to form network polymers  FR e) Types of Atoms in Polymer Backbone Homochain polymer : polymer chain (or backbone) consists of a single atom type Heterochain polymer : contain more than one atom type in the backbone f) Order of repeating units in backbone a) Homopolymer made from a single monomer b) Copolymer 1. Synthesis made from more than one type of monomer 2. Types of Copolymers i) Random Copolymer ii) Block Copolymer iii) Alternating Copolymer iv) Graft Copolymer  Classification of polymer FR Based on Based on Based on Based on types origin structure Polymerisation Types Synthetic Linear Elastomers polymers polymers Addition Thermo polymerisation Branch plastics Biopolymers Chain polymers Thermo- Condensation setting polymerisation Semi-synthetic polymers polymers Cross-linked polymers Classification by Origin: Synthetic polymers Synthetic polymers are human-made polymers. They can be classified into four main categories: thermoplastic, thermosets, elastomers, and synthetic fibers. They are commonly found in a variety of consumer products. The seven most common types of synthetic polymers are: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), p o l y s t y r e n e ( P S ) , n y l o n a n d Te f l o n ( P o l y t e t r a f l u o r o e t h y l e n e (PTFE)). Classification by Origin: Biopolymers Biopolymers are polymers that are biodegradable. Biodegradable means that these polymers c a n b e b r o ke n i n t o s m a l l s e g m e n t s. The polymers, which occur in nature are called natural polymer also known as biopolymers. Examples of such polymers a r e n a t u r a l r u b b e r, n a t u r a l s i l k , c e l l u l o s e , starch, proteins, etc..  Biopolymers FR ▪ Natural polymers ▪ Fibrin ▪ Collagen ▪ Chitosan ▪ Gelatin ▪ Hyaluronan ▪ Synthetic polymers ▪ PLA ; Polylactic acid ▪ PGA, Polyglycolic acid ▪ PLGA; Poly(lactic-co-glycolic acid) ▪ PCL; Polycaprolactone  Classification by Origin: FR Semi Synthetic polymers The polymers obtained by simple chemical treatment of natural polymers to change their properties Eg: Cellulose nitrate Classification by Structure: 1) Linear No branching other than the pendant groups associated with the monomer 2) Branched may have only a few side chains or may be every branch at every few repeating units 3) Network (Crosslinked) Crosslink density related to “hardness” An average of more than two Crosslinks per chain ⇒ infinite network Classification by Structure: Branched a) Star i) Star polymers consist of several linear polymer chains connected at one point. ii) uses: viscosity modifiers in high performance engine oils b) Dendrimer i) generation numbers up to 5-7 ii) near spherical shapes iii) Steric crowding gradient iv) uses: microencapsulation and drug delivery Classification by Structure: Branched c) Comb i) very high number of side chains, all of similar length ii) from Macromonomers such as 1-C20H40 (1-EICOSENE)  FR Classification Based on Polymerisation types The study of polymer science begins with understanding the methods in which these materials are synthesized. A chemical reaction that makes polymers is called a polymerisation Polymer synthesis is a complex procedure and can take place in a variety of ways.  FR Addition polymerisation Addition polymerization describes the method where monomers are added one by one to an active site on the growing chain. The polymers formed by the addition of monomers repeatedly without removal of by products. e.g., the formation of polyethylene from ethylene  FR Addition Polymerization A In* In A* A Initiation  FR Addition Polymerization Propagation A In* In A A* A Initiation  FR Addition Polymerization Propagation A In* In A A A* A Initiation  FR Addition Polymerization A nA In* In A A A A* In A A A A A* Initiation Propagation n *A A A A A *A A A A A m m In A A A A A In A A A A A A A A A A n n m Combination B A A A A m Disproportionation Termination Reactive site is consumed FR FR  FR Condensation polymerisation In a condensation polymerization, some atoms of the monomer do not end up in the polymer. They are formed by the combination of two monomers by removal of small molecules like water, alcohol or NH3. For example, When nylon 6,6 is made from adipoyl chloride and hexamethylene diamine, the chlorine atoms from the adipoyl chloride, each along with one of the amine hydrogen atoms, are expelled in the form of HCl gas. Eg: Nylon-6,6  FR Eg: Nylon-6,6 Since the reactants are in different phases, they can only react at the phase boundary. Once a layer of polymer forms, no more reaction occurs. Removing the polymer allows more reaction to occur. Adipoyl chloride in hexane Nylon 6,6 Diamine, NaOH, in H2O  FR Addition VS. Condensation Add a footer 28  FR Addition VS. Condensation Addition Condensation We call a polymerization a we call a condensation polymerization an polymerization if part of addition the monomer molecule is kicked out when the polymerization if monomer becomes part of the entire monomer the polymer. molecule becomes The part that gets kicked part of the polymer. out is usually a small molecule like water, or HCl gas. Types of Polymers Thermoset: cross-linked polymer that cannot be melted (tires, rubber bands). Thermoplastic: Melt able plastic. Elastomers: Polymers that stretch and then return to their original form: often thermoset polymers. Thermoplastics and Thermosets A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Thermoplastic polymers differ from thermosetting polymers since thermoplastics can be remelted and remolded. Thermosetting plastics when heated, will chemically decompose, so they can not be recycled. Yet, once a thermoset is cured it tends to be stronger than a thermoplastic. Typically, linear polymers with minor branched structures (and flexible chains) are thermoplastics. The networked structures are thermosets. 31  FR Examples of Thermoplastics Polymer ( )n ( )n ( )n ( )n Thermoplastic Properties FR Examples of Thermoset FR  FR Thermoset Properties  Elastomers FR Polymers that stretch and then return to their original form Add a footer 36  Elastomers FR Elastomers, can be a thermoplastic or a thermoset depending on the structure. They are excellent for parts requiring flexiblity, strength and durability. Such as automotive and industrial seals, gaskets and molded goods, roofing and belting, aircraft and chemical processing seals, food, pharmaceutical and semiconductor seals, and wire and cable coatings.  FR 7.2. Effect of Structural Modification and Temperature on Properties  FR Effect of Structural Modification  FR Effect of Temperature on Properties The response of a polymer to mechanical forces at elevated temperature is related to its dominant molecular structure. Tg is called the glass transition temperature. When the polymer is cooled below this temperature, it becomes hard and brittle, like glass. Some polymers are used above their glass transition temperatures, and some are used below. Hard plastics like polystyrene is used below its glass transition temperatures; that is in its glassy state. Their Tg's are well above room temperature, both at around 100 oC. Rubber elastomers like polyisoprene and polyisobutylene, are used above their Tg's, that is, in the rubbery state, where they are soft and flexible. 40  FR The glass transition temperature, Tg is not the same thing as melting temperature, Tm. Melting is a transition which occurs in crystalline polymers. Melting happens when the polymer chains fall out of their crystal structures, and become a disordered liquid. The Tg is a transition which happens to amorphous polymers; that is, polymers whose chains are not arranged in ordered crystals, but are just strewn around in any old fashion, even though they are in the solid state. The glass transition temperature (Tg) is a phenomenon of amorphous polymers. At this temperature, polymers undergo a transition from glassy to rubbery state. But even crystalline polymers will have a some amorphous portion. This portion usually makes up 40-70% of the polymer sample. This is why the same sample of a polymer can have both a glass transition temperature and a melting temperature. But you should know that the amorphous portion undergoes the glass transition only, and the crystalline portion undergoes melting only.  FR Polymer Crystallinity Polymers are rarely 100% crystalline Difficult for all regions of all chains to become aligned crystalline region Degree of crystallinity expressed as % crystallinity. -- Some physical properties depend on % crystallinity. -- Heat treating causes crystalline regions to grow and % crystallinity to increase. amorphous region 42 ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license. thermoplastics. The effect of temperature on the structure and behavior of FR